Lightning surge calculations including corona effects using a two-conductor model

The present paper describes a lightning surge calculation including the wave deformation due to corona. The corona wave deformation is represented by a linear corona model consisting of R-C parallel circuits with diodes, which is easily achieved by the electromagnetic transients program, EMTP. This simple corona model gives satisfactory accuracy compared with field test results. The lightning surge calculation was carried out using a two-conductor model consisting of a phase wire from which a back-flash occurs, and an equivalent ground wire. The two-conductor model gives almost the same accuracy as that using a multiconductor full representation model, for example an eight-conductor model for a twin-circuit line with two ground wires, with a computation time and memory less than a half those of the full representation model. It is observed from calculated results that the corona, in general, reduces voltages at towers and substations by more than 10%. The wave deformation due to the frequency-dependent effect of a transmission line generally has no significant effect on a lightning surge, and thus may be neglected in a lightning surge calculation.